I hesitate to use the term "guilty pleasure" because that's more when you know something is bad, or not that good, but enjoy it anyway. In this case I'm talking more about bands that you like and you get enjoyment out of, but other people are constantly surprised when they find out about it. Maybe you come off as the metal guy among your friends but have a fondness for Beatles, or something that breaks the mould so to speak.
While most friends know me as someone who listens to many different genres and musical styles, here are two bands that I like, that surprises people:
*Lacuna Coil - I haven't heard their last few albums, but their classic album run still holds up really well for me. Especially Unleashed Memories, Comalies and Karmacode. 3 Great albums that I return to somewhat frequently. I think it makes people surprised because most of the metal I listen to is either heavier or more experimental, and Lacuna Coil is really more of a straight up metalband, but I really like the melodies and despite never getting into any other goth metal with female vocals, LC really does it for me.
*Linkin Park - There's obviously an element of nostalgia involved. But it's more than that. The band evolved from their nu-metal roots and it's one of those bands where I'm happy to have grown up alongside the band also growing up. The teenager-phase is when you change the most as a person, and being able to still like something that I liked back then, I consider a win. Maybe if I heard them for the first time today, I wouldn't like them as much, but I've still liked every album they put out after the classic ones, so that's something.
Neither of these would necessarily end up high on a topX favorite list, but I'm still more than ~1500 plays on lastfm with both.